1. Field of the Invention
The present invention relates to a plate supplying apparatus, and more particularly to a plate supplying apparatus for supplying a plate, which is transferred such that its faces are reversed, from a storage section in which a plurality of plates are piled such that each plate alternates with a slip sheet.
2. Related Art Statement
A conventional plate supplying apparatus automatically supplies a plate, such as a presensitized (PS) plate, to an image recording apparatus for irradiating that plate with a laser beam to directly record an image thereon. The plate used with such an image recording apparatus includes a support layer and an image recording layer. Since the image recording layer is easily damaged, the utmost caution is required when supplying the plate. In recent years, a variety of types of plates having a thickness between 0.15 millimeters (mm) and 0.50 mm have come into wide use.
The conventional plate supplying apparatus receives a cassette containing a plurality of plates each alternating with a slip sheet for preventing friction between plates. For example, Japanese Patent Laid-Open Publication No. 2000-247489 discloses a plate supplying apparatus which includes a movable arm or the like having plate suction cups. In the state where the plate suction cups secure a support layer side of a plate via suction, the movable arm moves the plate suction cups to a prescribed position, so that the plate is taken out from a cassette, and then supplied to an image recording apparatus as described above. Each time the movable arm or the like takes a plate out from the cassette, movable slip sheet suction cups secure a slip sheet via suction. In this state, the slip sheet suction cups move to a prescribed position, thereby ejecting the slip sheet from the conventional plate supplying apparatus.
Referring to FIGS. 23 to 26, an operation of the above-described conventional plate supplying apparatus will be described. FIGS. 23 to 26 are views used for explaining a series of operation of a plate transfer mechanism which is included in a plate supplying apparatus 200 and used for transferring plates P from a cassette 206 toward an image recording apparatus.
In FIGS. 23 to 26, the plates P to be supplied from the plate supplying apparatus 200 are stored in the cassette 206 such that an image recording layer of each plate P faces downwards. The plates P are piled in the cassette 206 in a manner as described above, i.e., each plate P alternates with a slip sheet S. The plate transfer mechanism included in the plate supplying apparatus 200 transfers the plates P from the cassette 206 placed in a plate supply position to the image recording apparatus. The plate transfer mechanism includes a traveling member 204 which travels along a guide rail 210 by receiving drive from an endless synchronous belt 207 which is caused to move rotationally by drive of a motor 208 transmitted via a belt 209. The traveling member 204 has a coupling member 205 secured thereon. The coupling member 205 holds the synchronous belt 207 by sandwiching the synchronous belt 207 between two separate portions so as to receive the drive therefrom. The traveling member 204 also includes a speed reducer 203 having a pinion to be engaged with a rack rail 211 provided in parallel with the guide rail 210. The speed reducer 203 has an arm 202 secured on an output shaft thereof. The arm 202 has an end portion including a support board on which a plurality of suction pads 201 are provided for holding a plate P via suction. The plurality of suction pads 201 are provided so as to conform to the plates P stored in the cassette 206.
In the case where the plate transfer mechanism having the above-described structure is in the state illustrated in FIG. 23, when the traveling member 204 is driven by the motor 208 so as to move toward a direction to the right (hereinafter, referred to as the “transfer movement direction”), as illustrated in FIGS. 24–26, the arm 202 pivots on the center of the output shaft of the speed reducer 203 in a clockwise direction (hereinafter, referred to as the “transfer turn direction”). Therefore, in the case where the suction pads 201 hold a support layer side of a plate P via suction in the state illustrated in FIG. 23, and then, as illustrated in FIGS. 24–26, the traveling member 204 is driven by the motor 208 so as to move toward the transfer movement direction, when the arm 202 pivots 180° in the transfer turn direction, the plate P held via suction by the suction pads 201 is turned, such that the plate's faces are reversed (i.e., the support layer of the plate P faces downwards), while experiencing bending stress. Thereafter, as illustrated in FIG. 26, a leading end of the plate P will be sandwiched between a pair of transfer rollers 212 and 213 for transferring the plate P to the image recording apparatus.
In some cases, when the arm 202 transfers the plate P, a slip sheet S adhering to a back face of the plate P can also be transferred together depending on the type of the slip sheet S and an environmental condition such as static electricity. In order to solve such a problem, the plate supplying apparatus 200 disclosed in Japanese Patent Laid-Open Publication No. 2000-247489 performs, for example, a so-called separating operation during transfer of the plate P held via suction by the suction pads 201 by causing the plate P to stand still, or vibrate, for a prescribed period, thereby peeling off the slip sheet S adhering to the back face of the plate P.
Referring to FIG. 27, described next is an exemplary operation of peeling off the slip sheet S by swinging the arm 202 for a prescribed time period. FIG. 27 is a graph illustrating movements of the arm 202 swinging for a prescribed time period with respect to the speed of the traveling member 204 moving toward the transfer movement direction and the angle of the arm 202 in the transfer turn direction. In FIG. 27, the speed of the traveling member 204 moving from the position in FIG. 23 toward the transfer movement direction is indicated by a positive value, and the angle of the arm 202 in the transfer turn direction is indicated on the assumption that the arm 202 in the state of FIG. 23 is set at an angle of 0°.
In FIG. 27, when the arm 202 is placed at 0° in the transfer turn direction, a plate P is held via suction by the suction pads 201 (the state of FIG. 23). Then, the traveling member 204 moves toward the transfer movement direction until the arm 202 reaches an angle a. Thereafter, in a section from the angle a to an angle b, the traveling member 204 repeatedly makes a slight movement toward the transfer movement direction and a pause. When the arm 202 reaches the angle b, the traveling member 204 moves backwards in an anti-transfer movement direction until the arm 202 returns to the angle a. Then again, in the section from the angle a to the angle b, the traveling member 204 repeatedly makes a slight movement toward the transfer movement direction and a pause. The plate supplying apparatus 200 repeats the above-described operation a prescribed number of times, and thereafter transfers the plate P held via suction by the suction pads 201 toward the image recording apparatus in a manner as described above.
However, in such a conventional plate supplying apparatus 200 which is configured to peel off the slip sheet S adhering to the back face of the plate P by causing the plate P to stand still for a prescribed time period during transfer, the reliability of peeling off the slip sheet S is low. In some cases, the slip sheet S adhering to the back face of the plate P can be transferred together with the plate P.
In the above-described case of peeling off the slip sheet S adhering to the back face of the plate P by swinging the arm 202 for a prescribed time period, it is necessary to increase the angle b in order to reliably peel off the slip sheet S. For example, the separating operation is performed with settings of the angle a=10° and the angle b=40°. When the separating operation is performed with such angle settings, bending stress is generated by the stiffness of the plate P in accordance with the angle of the arm 202. The bending stress pushes the plate P toward the direction of the cassette 206. As described above, in the section from the angle a to the angle b, vibration is applied to the plate P. Accordingly, the pushing force due to the bending stress and the vibration are simultaneously applied to the plate P, and therefore, in some cases, friction is caused between pushed portions of the plate P, resulting in damage to an image recording layer of the plate P.
In recent years, there have been needs of plates having a large area and/or a large thickness, and simultaneous supply of a plurality of such plates, for example. In the case of using the conventional plate supplying apparatus 200 to transfer such plates having a large area and/or a large thickness, a large moment of force is applied to the arm 202. Therefore, a drive force of the motor 208 for driving the traveling member 204 is required to be increased, resulting in a cost increase.
Further, in the case of using the conventional plate supplying apparatus 200 to transfer the plate P, bending stress is applied to the plate P in a manner as described above, and therefore, a repulsive force is generated in a direction of causing the plate P to be detached from the suction pads 201. Such a repulsive force becomes larger with an increase of the thickness of the plate P. For example, in the case of transferring a plate P having a thickness of 0.4 mm, the repulsive force is large as compared to the suction force of the suction pads 201, and therefore, in some cases, the plate P can be dropped from the suction pads 201 during transfer.
In order to prevent such a drop of the plate P, it is conceivable to increase a pivoting radius of the suction pads 201 to reduce the repulsive force. In such a case, for example, the arm 202 is required to be lengthened, resulting in upsizing of the plate transfer mechanism. Moreover, the drive force of the motor 208 is required to be increased, leading to the upsizing and cost increase of the plate supplying apparatus 200.
In order to prevent the drop of the plate P, it is also conceivable to set the suction force of the suction pads 201 so as to exceed the repulsive force by increasing negative pressure supplied to the suction pads 201. However, in the case of using a large suction force, which has been set so as to exceed the repulsive force, in order to secure a plate P having a small thickness (e.g., 0.15 mm) via suction, the plate P having such a small thickness may be deformed by such a large suction force. Accordingly, it is necessary to control the negative pressure supplied to the suction pads 201 in accordance with the thickness of the plate P to be transferred. Thus, a mechanism for detecting the thickness of the plate P and a mechanism for controlling the negative pressure are required, leading to a cost increase of the plate supplying apparatus 200.